• Structural Engineering and Mechanics
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• 제59권2호
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• pp.291-312
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• 2016

Seismic performance evaluation of shear wall is essential as it is the major lateral load resisting member of a structure. The ultimate load and ultimate drift of the shear wall are the two most important parameters which need to be assessed experimentally and verified analytically. This paper comprises the results of monotonic tests, quasi-static cyclic tests and shake-table tests carried out on a midrise shear wall. The shear wall considered for the study is 1:5 scaled model of the shear wall of the internal structure of a reactor building. The analytical simulation of these tests is carried out using micro and macro modeling of the shear wall. This paper mainly consists of modification in the hysteretic macro model, developed for RC structural walls by Lestuzzi and Badoux in 2003. This modification is made by considering the stiffness degradation effect observed from the tests carried out and this modified model is then used for nonlinear dynamic analysis of the shear wall. The outcome of the paper gives the variation of the capacity, the failure patterns and the performance levels of the shear walls in all three types of tests. The change in the stiffness and the damping of the wall due to increased damage and cracking when subjected to seismic excitation is also highlighted in the paper.

• Structural Engineering and Mechanics
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• 제40권5호
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• pp.655-663
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• 2011

Asbestos-cement is a material with valuable strength and durability. It was extensively used for water distribution pipes across the world from the 1950s until the early 1980s. The network of pipes in this case study dates from the 1970s, and after more than 30 to 40 years of service, some pipes have been found to break under common service pressure with no apparent reason. A set of mechanical tests was performed including bending, compression, pressure and crushing tests. Microscopy analysis was also used to understand the material behaviour. Tests showed that there was a clear loss of strength in the pipes and that the safety factor was under the established threshold in most of the specimens. Microscopy results showed morphological damage to the pipes. The loss of strength was attributed to a leaching effect. Leaching damages the cement matrix and reduces the frictional interfacial shear stress.

• 마이크로전자및패키징학회지
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• 제16권3호
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• pp.45-51
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• 2009

본 연구에서는 습식 방법으로 진행 되는 BGA 현상 공정에 있어 기존의 수평 장비를 대체하여 수직 장비를 개발하였다. 지그를 이용하여 기판을 수직 방향으로 고정한 후 습식 공정을 진행함으로써 기존 수평 장비의 단점인 롤러와 기판 표면 회로 패턴의 충돌로 인한 회로 패턴 손상 문제를 원천적으로 제거하고자 하였다. 개발된 수직 장비의 공정 특성을 수평 장비와 비교 평가 하기 위하여 유니포미터 측정, 회로 패턴 손상 평가 및 불량 평가의 실험을 수행하였다. 평가 결과 수직 장비의 유니포미티 특성은 수평 장비와 동일한 수준이며 중력 방향의 액흐름에 대한 공정 특성 영향은 미미한 것으로 확인 되었다. 또한, 수평 장비 대비 $3{\sim}4{\mu}m$ 더 미세한 회로 패턴에 대해여 손상 없이 공정을 진행 할 수 있음을 확인 할 수 있었다.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 1999년도 춘계 학술발표회 논문집
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• pp.171-176
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• 1999

Nondestructive inspection and accompanying life analysis based on fracture mechanics were the major conventional methods for evaluating remaining life of critical high temperature components in power plants. By using these conventional methods, it has been difficult to perform in-service inspection for life prediction. Also, quantitative damage evaluation due to unexpected abrupt changes in operating temperature was almost impossible. Thus, many efforts have been made for evaluating remaining life during operation of the plants and predicting real-time life usage values based on the shape of structures, operating history, and material properties. In this study, a core software for on-line life monitoring system which carries out real-time life evaluation of a critical component in power boiler(high temperature steam headers) is developed. The software is capable of evaluating creep and fatigue life usage from the real-time stress data calculated by using temperature/stress transfer Green functions derived for the specific headers and by counting transient cycles. The major benefits of the developed software lie in determining future operating schedule, inspection interval, and replacement plan by monitoring real-time life usage based on prior operating history.

• 터널과지하공간
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• 제30권1호
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• pp.1-14
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• 2020

미소진동 모니터링은 구조물의 미세 수준의 손상을 감지하여 구조물의 성능확인 및 안전관리에 활용된다. 신뢰도 높은 미소진동 모니터링 시스템을 구성하기 위해서는 수집된 신호를 변환하는 시그널 컨디셔너의 역할이 매우 중요하다. 시그널 컨디셔너는 정확한 데이터 수집과 기기 정밀 제어에 도움을 주며 신호변환, 선형화, 증폭 등의 추가적인 기능을 수행한다. 본 기술보고는 기존에 개발한 미소진동 모니터링 시스템의 성능을 향상하여 보다 정밀한 모니터링 구현을 목적으로 광산현장에 적합한 노이즈 저감형 시그널 컨디셔너를 개발하고 이를 검토하였다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 추계 학술발표회논문집
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• pp.303-310
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• 2003

Small-scale models have been frequently used for experimental evaluation of seismic performance because of limited testing facilities and economic reasons. However, there are not enough studies on similitude law for analogizing prototype structures accurately with small-scale models, although conventional similitude law based on geometry is not well consistent in the inelastic seismic behavior. When fabricating prototype and small-scale model of reinforced concrete structures by using the same material, added mass is demanded from a volumetric change and scale factor could be limited due to size of aggregate. Therefore, it is desirable that different material is used for small-scale models. Thus, a modified similitude law could be derived depending on geometric scale factor and equivalent modulus ratio. In this study, compressive strength tests are conducted to analyze equivalent modulus ratio of micro-concrete to normal-concrete. Equivalent modulus ratios are divided into elastic, weak nonlinear and strong nonlinear phases, which are based on ultimate strain level. Therefore, an algorithm adaptable to the pseudodynamic test, considering equivalent three phase similitude law based on seismic damage levels, is developed. In addition, prior to tile experiment, it is verified numerically if tile algorithm is applicable to the pseudodynamic test.

• Structural Engineering and Mechanics
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• 제73권4호
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• pp.447-454
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• 2020

Seismic isolation technology has a wide application to protect bridges from earthquake damage, a new designed bridge pier with seismic isolation are provided for railways in seismic regions of China. The pier with rocking isolation is a self-centering system under small and moderate earthquakes, and the unbonded prestressed tendons are used to prevent overturning under strong earthquakes. A numerical model based on pseudo-static testing results is presented to evaluate the seismic performance of isolation bridge piers, and is validated by the shaking table test. It is found that the rocking response and the loss of prestressing for the bridge pier increase with the increase of earthquake intensity. Besides, the intensity and spectral characteristics of input ground motion have great influence on displacement of the top and bottom of the bridge pier, while have less influence on the bending moment of the pier bottom. Experimental and numerical results show that the rocking-isolated piers presented in this study have good seismic performance, and it provides an alternative way for the railway bridge in the regions with high occurrence of earthquakes. Therefore, we provide the detailed procedures for seismic design of the rocking-isolated bridge pier, and a case study of the seismic isolation design with rocking piers is carried out to popularize the seismic isolation methods.

• Structural Engineering and Mechanics
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• 제19권3호
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• pp.261-279
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• 2005

The hot spot stress approach is usually adopted in the fatigue design and analysis of tubular welded joints. To apply the hot spot stress approach for fatigue evaluation of long span suspension bridges, the FEM is used to determine the hot spot stress of critical fatigue location. Using the local finite element models of the Tsing Ma Bridge, typical joints are developed and the stress concentration factors are determined. As a case for study, the calculated stress concentration factor is combined with the nominal representative stress block cycle to obtain the representative hot spot stress range cycle block under traffic loading from online health monitoring system. A comparison is made between the nominal stress approach and the hot spot stress approach for fatigue life evaluation of the Tsing Ma Bridge. The comparison result shows that the nominal stress approach cannot consider the most critical stress of the fatigue damage location and the hot spot stress approach is more appropriate for fatigue evaluation.

• Structural Engineering and Mechanics
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• 제55권6호
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• pp.1177-1202
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• 2015

In this paper, a new intensity measure of earthquakes for probabilistic seismic analysis is presented for skewed highway bridges. Three different cases of skewed bridges with different skew angles ($0^{\circ}$, $30^{\circ}$ and $45^{\circ}$) are considered. Well-known intensity measures (e.g., PGA, $S_a$) are evaluated and critically discussed based on sensitivity analysis: efficiency, practically, proficiency and sufficiency of intensity measures are considered in detail. The analyses demonstrated that the intensity measures have to take into account structural acceleration on a wide range of periods so that a new seismic intensity measure is proposed showing that it has less dispersion compared to others. Since the proposed intensity represents the average value of the $S_a$ (between a lower and upper structural period) it has been called Averaged Spectral Acceleration (ASA). Based on performed incremental dynamic analysis (IDA), the seismic analytical fragility curves of typical skewed highway bridges have been evaluated for different states of damage controlling the low dispersion of the ASA index as well as its proficiency and sufficiency.

• Earthquakes and Structures
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• 제10권1호
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• pp.125-139
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• 2016

For seismic retrofitting of masonry walls, the use of fibre reinforced cement-based mortar for bonding the fibre grids can eliminate some of the shortcomings related to the use of resin as bonding material. The results of an experimental testing program on masonry walls retrofitted with fibre reinforced mortar and fibre grids are presented in this paper. Seven squat masonry walls were tested under unidirectional lateral displacement reversals and constant axial load. Steel anchors were used to increase the effectiveness of the bond between the fibre grids and the masonry walls. Application of fibre grids on both lateral faces of the walls effectively improved the hysteretic behaviour and specimens could be loaded until slip occurred in the horizontal joint between the masonry and the bottom concrete stub. Application of the fibre grids on a single face did not effectively improve the hysteretic behaviour. Retrofitting with fibre reinforced mortar only prevented the early damage but did not effectively increase deformation capacity. When the boundaries of the cross sections were not properly confined, midplane splitting of the masonry walls occurred. Steel anchors embedded in the walls in the corners area effectively prevented this type of failure.